The speed of a boat in still water is 20 mph. it travels from one pier to another with the current in 4 hours and back against the current in 6 hours and 40 minutes. if the distance between piers is 100 miles, what is the speed of the current

The answer is, "the speed of the current is 5 miles per hour."

To calculate the speed of the current,
let's assume speed of current =  xmph. Time taken to travel from one pier to another with the current = 100/(20+x)h

But the time taken to travel from one pier to another with the current, which is given is = 4 hours. So,  4=100/(20+x) 80+4x = 100

4x = 20

x = 5 Thus, the speed of the current is 5 miles per hour.